Desalination can be accomplished using a number of techniques. These may be classified as thermal processes that involve phase change such as Multi Stage Flash, membrane processes that do not involve phase change such as Reverse Osmosis (RO), and hybrid processes that involve both membrane and phase change such as membrane distillation. Currently, reverse osmosis (RO) is the standard approach to desalinate seawater. About 60% of the worldwide installed desalination capacity is based on RO.
However, persisting challenges of the RO technology limit its wider acceptance. These challenges include the following. (1) The diameter of the pores of the RO membranes is less than 1 nm. Therefore, the pores are prone to clogging and fouling, requiring the regular replacement of the RO membranes, which in turn increases the operating costs and complexity of such systems. (2) In the RO process, the saltwater is forced through these very small pores of the membranes. Further, there are large osmotic pressures working against the desalination. Overcoming both sources of resistance requires the consumption of significant amount of electrical energy. (3) The required electrical energy is typically generated by burning fossil fuels, which in turn further accelerates global warming that caused the water shortage in the first place. (4) In many developing countries, the power grid is unreliable. Therefore, the operation of grid-dependent RO desalination system is unreliable in these countries. For at least the above reasons, there is a pressing need to develop alternatives to the RO desalination technology. Some of these solutions need not replace RO in every possible application space. Rather, they can offer a competitive alternative to RO in some specific application niches, and thus could coexist with RO.